
//线条：开始xy坐标，结束xy坐标，线条透明度
function Line(x, y, _x, _y, o) {
    this.beginX = x;
    this.beginY = y;
    this.closeX = _x;
    this.closeY = _y;
    this.o = o;
}
//点：圆心xy坐标，半径，每帧移动xy的距离
function Circle(x, y, r, moveX, moveY) {
    this.x = x;
    this.y = y;
    this.r = r;
    this.moveX = moveX;
    this.moveY = moveY;
}
//生成max和min之间的随机数
function num(max, _min) {
    var min = arguments[1] || 0;
    return Math.floor(Math.random() * (max - min + 1) + min);
}
// 绘制原点
function drawCricle(cxt, x, y, r, moveX, moveY) {
    var circle = new Circle(x, y, r, moveX, moveY);
    cxt.beginPath();
    cxt.arc(circle.x, circle.y, circle.r, 0, 2 * Math.PI);
    cxt.closePath();
    cxt.fill();
    return circle;
}
//绘制线条
function drawLine(cxt, x, y, _x, _y, o) {
    var line = new Line(x, y, _x, _y, o);
    cxt.beginPath();
    cxt.strokeStyle = 'rgba(0,0,0,' + o + ')';
    cxt.moveTo(line.beginX, line.beginY);
    cxt.lineTo(line.closeX, line.closeY);
    cxt.closePath();
    cxt.stroke();

}
//初始化生成原点
function init() {
    circleArr = [];
    for (var i = 0; i < POINT; i++) {
        circleArr.push(drawCricle(context, num(WIDTH), num(HEIGHT), num(15, 2), num(10, -10) / 40, num(10, -10) / 40));
    }
    draw();
}

//每帧绘制
function draw() {
    context.clearRect(0, 0, canvas.width, canvas.height);
    for (var i = 0; i < POINT; i++) {
        drawCricle(context, circleArr[i].x, circleArr[i].y, circleArr[i].r);
    }
    for (var i = 0; i < POINT; i++) {
        for (var j = 0; j < POINT; j++) {
            if (i + j < POINT) {
                var A = Math.abs(circleArr[i + j].x - circleArr[i].x),
                    B = Math.abs(circleArr[i + j].y - circleArr[i].y);
                var lineLength = Math.sqrt(A * A + B * B);
                var C = 1 / lineLength * 7 - 0.009;
                var lineOpacity = C > 0.03 ? 0.03 : C;
                if (lineOpacity > 0) {
                    drawLine(context, circleArr[i].x, circleArr[i].y, circleArr[i + j].x, circleArr[i + j].y, lineOpacity);
                }
            }
        }
    }
}
function start(){
    //定义画布宽高和生成点的个数
    WIDTH = window.innerWidth,
    HEIGHT = window.innerHeight,
    POINT = 35;

    canvas = document.getElementById('Bgcanvas');
    canvas.width = WIDTH;
    canvas.height = HEIGHT;
    canvas.style.backgroundColor = '#e7f4fd';
    // window.onload = function () {
    // let WIDTH = documment.body.clientWidth || document.documentElement.clientWidth;
    // let HEIGHT = documment.body.clientHeight || document.documentElement.clientHeight;
    // canvas.width = WIDTH;
    // canvas.height = HEIGHT;
    // }
    context = canvas.getContext('2d');

    context.strokeStyle = 'rgba(0,0,0,0.08)',
    context.strokeWidth = 3,
    context.fillStyle = 'rgba(0,0,0,0.15)';
    circleArr = [];
    init();
    setInterval(function () {
        for (var i = 0; i < POINT; i++) {
            var cir = circleArr[i];
            cir.x += cir.moveX;
            cir.y += cir.moveY;
            if (cir.x > WIDTH) cir.x = 0;
            else if (cir.x < 0) cir.x = WIDTH;
            if (cir.y > HEIGHT) cir.y = 0;
            else if (cir.y < 0) cir.y = HEIGHT;

        }
        draw();
    }, 16);
}
var WIDTH,HEIGHT,POINT,canvas,context,circleArr;
start();
//调用执行
window.onresize = function () {
    start();
}
